the alpha value, in [0, 1], for the colours of
oce.colorsTwo.

Details

A family of nine-colour schemes is as follows: which="jet" (or
which="9A" or which=9.01 for the Jet scheme; which="9B"
or which=9.02 for a scheme similar to Jet but omitting the green, and
somewhat desaturating the yellow and cyan.

oce.colorsGebco provides palettes that mimic the GEBCO atlas colours,
with shades of blue for water and of brown for land. The blue values go
from dark to light, and the brown ones from light to dark; in this way,
topographic images have light values near sea-level, and get darker in
either deeper water or higher terrain.

oce.colorsJet provides a palette similar to the Matlab “jet”
palette.

oce.colorsTwo provides a two-tone palette that fades to white at
central values.

oce.colorsViridis provides a matplotlib (python) colour scheme that
became the standard in 2015; see [2]. This is a blue-yellow transition that
is designed to reproduce well in black-and-white, and also to be
interpretable by those with certain forms of colour blindness [3, 4, 5].

oce.colorsCDOM, oce.colorsChlorophyll,
oce.colorsDensity, oce.colorsFreesurface,
oce.colorsOxygen, oce.colorspAR, oce.colorsPhase,
oce.colorsSalinity, oce.colorsTemperature,
oce.colorsTurbidity, oce.colorsVelocity and
oce.colorsVorticity are based on RGB values set up by Kristen M.
Thyng for her Python package named cmcolor [7].

[6] The Geography department at the University of Oregon has good resources
on colour schemes; see e.g.
http://geography.uoregon.edu/datagraphics/color_scales.htm (This URL
worked prior to December 8, 2015, but was found to fail on that date; it is
included here in case users want to search for themselves.)